Cathode ray tube display system for color television



D. B. SMITH Jan. 24, 1961 CATHODE RAY TUBE DISPLAY SYSTEM FOR COLOR TELEVISION Filed June 14, 1952 2 Sheets-Sheet 1 Jan. 24, 1961 CATHODE Filed June 14, 1952 D. B. SMITH 2,969,423 RAY TUBE DISPLAY SYSTEM FOR coLoR TELEVISION 2 Sheets-Sheet 2 l l i l l l l D l l i l i V I l" I I l i l g F/Qz 5. I l I I I l 1 l I i i i i l I I I g 1 I l l l I9 I. l 1 I i l l im l l 1 g| I I' I n :WW1 .so Hawai I v I I la .l l Ja [502/05 n30 5oz/a' 33a' a INVENTOR. D/W/D -5777/777' @rra/wey 'CATHODE RAY TUBE DISPLAY SYSTEM FOR COLOR TELEVISION David B. Smith, Meadowbrook, Pa., assignor to Philco Corporation, Philadelphia, Pa., a corporation vof Penn- Sylvania FiledJune 14, 1952, Ser. No. 293,564

16 Claims. (Cl. 178-5.4)

The present invention relates to electrical systems and more particularly, to cathode-ray tube systems for producing a color television image.

In one form, cathode-ray tubes for producing a color television image may comprise an image screen made up of a plurality of parallel stripes of fluorescent material arranged on a suitable base. such as the'faceplate of the tube. The stripes may be disposed in groups so that each group of stripesV is adapted to produce light of' the different primary colors. In an alternative arrangement of the image screen, the faceplate of the cathode-ray tube may be provided with a continuous coating of a fluorescent material producing one of the primary colors. The fluorescent materials producing the remaining two primary colors may be deposited on Vane-like elements arranged adjacent to the faceplate with their longitudinal axes parallel to the faceplate and their surfaces substantially perpendicular to the faceplate.

For proper color rendition, it is required. that the phosphor portions of the image screenproducing each of the primary colors of light be impinged by the cathode-ray beam in synchronism with the contemporaneous value of the video signal which represents the corresponding color component of the televised image and which varies the intensity of the beam proportionally to the amplitude of the color component.

To achieve a synchronous relationship between the contemporaneous value of the image signal and the impingement of the beam on the corresponding phosphor portion, it has been proposed further to provide the cathode-ray tube with an auxiliary deflection system suitably energized so that the beam, during its normal scanning cycle, is made to impinge selectively on the appropriate portion of the image screen. More particularly, in the case off a cathode-ray tube having a screen provided with laterally arrangedphosphor stripes as above described, it has been proposed to provide such tubes with an auxiliary beam deflecting system comprising paired groups of spaced deflection wire or plate-shaped electrodes arranged adjacent and parallel to the phosphor stripes. By applying a deflection signal to adjacent pairs of electrodes, an auxiliary deflection may be impressed on the cathode-ray beam as it scans the image screen to cause the beam to impinge on selected portions of the phosphors of the image screen in synchronism with the occurrence of the color information contained in the applied image signal. In the alternative arrangement above described in which the phosphors producing two of the primary colors are deposited on vane like elements arranged adjacent to the faceplate which carries the phosphor producing the third primary color, the vanes may be made of electrically conducting material and thereby made further to serve asy the auxiliary deflection elements. By applying a control signal to adjacent pairs of vanes, the beam may be made to impinge on one or the other of the vanes and the superimposed phosphor, or on the faceplate exposed to the beamY between the vanes.

atent Patented Jan. 24, 1961 To achieve a desired degree of image definition comparable to that now commonly available in so-called blackand-white image reproducers, the image reproducing screen of the cathode-ray tube should contain a relatively large number of groups of the phosphor portions. In the case of a cathode-ray tube screen constituted of vertically arranged groups of phosphor stripes, scanned in sequence by a normally horizontally scanning beam, the number of groups of phosphor stripes should at least equal the number of picture elements containedv in one line scan of the reproduced image and in a typical case there may be 400 or more groups of phosphor stripes arranged on the screen of the cathode-ray tube. For selectively exciting the individual phosphor stripes of the groups, a corresponding number of pairs of the auxiliary deflection electrodes are required. i

The deflection electrodes so required effectively constitute a capacitor, the capacitance of which is determined by the number of the pairs of electrodes, the spacing between adjacent electrodes and the dimensions of the electrodes. In the case of a cathode-ray tube adapted to produce an image 12" x 16"'in size and containing an auxiliary deflection system made up of parallel wires arranged in 400 to 450 pairs, the deflection system may have a capacitance of the order of 5,000 micromicrofarads. When the deflection signal has a frequency of the order of 7 mc./scc., such as would be required to achieve the desired color detail from such a screen structure, the above noted capacitance value corresponds to a reactive impedance of the order ofv 10 ohms. Since the peakvalue of the deflection voltage required may be of the order of 100 to 200 volts, a considerable problem arises in supplying the necessaryy energy to the auxiliary deflection system. v

It has been proposed to supply this energy by means of wide band amplifiers energized by an appropriatefcontrol quired, its high cost, and the substantially purely reactiver nature of the deflection system serving as a load for the amplifier. A further difficulty is that the transit time of the control signal through the amplifier normally introduces a phase shift of the signal, which, unless special precautions are taken, may have a variable character so that proper synchronization between the contemporaneous value of the video color information and the impingement of the beam on'the phosphor stripes-,of a particular color is not maintained throughout the scanning area of the screen.

Another important disadvantage of such a prior proposal is that it is necessary to make the load impedance of the wide band amplifier with a relatively low Q value in order to makethe deflection voltage substantially independent of the frequency of the deflection signal. In a system of the type above described, it may thus be necessary to shunt thefdeflection systemwith a resistor of the order of 10 ohms` in which case, a power of the order of several kilowatts must be supplied to the load impedance to achieve the desired deflection voltage.

It is an object of the invention to provide a low cost and simple system for synchronizing thev color determining deflection system of aA color television cathode-ray tube with the color information-applied to the tube.

A further object of the invention is to provide a color determining deflection system of the foregoing type, whichy system is substantially free of phase shiftsv between the color determining deflection system of the cathode-ray 0 tube and the color information supplied to the tube;

image reproducer which system operates under narrow band conditions and at high Q values and which requires only small amounts of power from its energizing source.

Further objects of the invention will appear as the specification progresses.

In accordance with the invention, the foregoing objects are achieved, in a color television system comprising a cathode-ray tube having auxiliary deflection means arranged to deflect the scanning beam onto selected portions of the screen in synchronism with recurring time-spaced color image information applied to the beam, by actuating the deection system independently of the color image information and by deriving from the dellection system a control quantity by means of which the time-spaced color image information applied to the beam is appropriately modified to the requirements of the deflection system. More specifically, in an embodiment of the invention in which the image screen of the cathode-ray tube reproducer is constituted by vertical stripes of luminescent materials which produce light of three different primary colors, and in which the auxiliary deflection system comprises a plurality of pairs of deflection electrodes arranged in the vicinity of the screen, the deflection elements are energized by a separate signal source in the form of an oscillator including the deection electrodes as a circuit component thereof, and the color image signal applied to the beam is modied to the requirements of the deflection signal by means of a control signal derived from the oscillator source.

Since the auxiliary deflection system is energized independently of the color image information, the system may be operated under narrow band conditions, i.e. may be operated as a resonant system having a Q value of the order of 100 or more, so that only a small amount of power is consumed in achieving the desired deflection voltage.

-The invention will be described in further detail with reference to the appended drawings forming part of the specification and in which:

Figure 1 is a block diagram, partially schematic, showing one form of a color television image reproducing system in accordance with the invention;

Figure 2 is a perspective view of a portion of one form of an image screen structure suitable for the cathode-ray tube systems of the invention; and

Figure 3 is a graph showing the waveforms of certain signals appearing in the system shown in Figure l.

Referring to Figure 1, the cathode-ray tubersystem there shown comprises a cathode-ray tube containing, Within an evacuated envelope 12, a conventionally constructed beam generating and accelerating electrode system comprising a cathode 14, an electrode 16 for varying the intensity of the beam, a focusing electrode 18 and a beam accelerating electrode 20, the latter of which may consist of a conductive coating arranged on the inner wall of the envelope and terminating at a point spaced from the end faceplate 22 of the tube in conformance with well established practice. Suitable means (not shown) are provided for maintaining the cathode 14 at its operating temperature, The electrode system so defined is energized from a suitable source of potentials shown as a battery 24 having its negative pole connected to a point at ground potential and its positive pole connected to the electrode 20, and having an appropriately positioned tap to which the electrode 18 is connected.

A deflection yoke 26, coupled to horizontal and vertical deflection signal generators 27 and 28, is provided for deecting the generated electron beam across the faceplate 22 of the cathode-ray tube to form a raster thereon. The generators 27 and 28 may be of conventional form and the generator 28 may include an AFC system by means of which the horizontal scanning' frequency is maintained at a constant value irrespective of minor variations of the applied horizontal synchronizing pulses and/or the presence of interference signals in ac' 4 cordance with the usual practice in monochrome television receivers.

The end face 22 of the tube is provided with a beam intercepting structure, one suitable form of which is shown as 30 in Figure 2. In the arrangement shown in Figure 2, the structure 30 is formed directly on the faceplate 22. However, the structure 30 may alternatively be formed on a suitable light transparent base which is independent of the faceplate 22 and may be spaced therefrom. In the arrangement shown, the faceplate 22, which in practice consists of glass having preferably substantially uniform transmission characteristics for the various colors of the visible spectrum, is provided with a plurality of parallelly arranged stripes 32, 34 and 36 of phosphor materials which, upon impingement of the cathode-ray beam, uoresce to produce light of three different primary colors. For example, the stripes 32 may consist of a phosphor such as zinc phosphate containing manganese as an activator, which upon electron impingement produces red light, the stripes 34 may consist of a phosphor such as zinc orthosilicate, which produces green light, and the stripes 36 may consist of a phosphor such as calcium magnesium silicate containing titanium as an activator, which produces blue light. Other suitable materials for the phosphor stripes 32, 34 and 36, as well as methods of applying the same to the faceplate 22, are well known to those skilled in the art, and further details concerning the same are believed to be unnecessary.

For reasons later to be more fully pointed out, the red and blue stripes 32 and 36 respectively have a width substantially equal to twice the width of the green stripes 34, and the stripes are arranged in the sequence R--G-B-G-R-G-B, so that a green light producing stripe appears adjacent to each of the red and blue light producing stripes.

The stripes 32, 34 and 36 may be provided with a thin, electrically conductive, electron permeable layer 38, the purpose of which will be pointed out later. Preferably the layer 38 consists of an electron permeable aluminum coating which also serves as a mirror for reflecting light generated by the phosphor stripes. External electrical connection to the coating 38 may be provided by means of a terminal lead 39.

Arranged close to the phosphor stripes is a color determining deection system comprising spaced interleaved pairs of Wire elements 40 and 42 arranged parallel to the phosphor stripes and positioned so that the projections thereof pass through the center line of the red and blue stripes 32 and 36 respectively. Wire elements 40 are interconnected by a common bus 44 terminating at a connection point 48 external to the tube 10, whereas wire elements 42 are interconnected by a common bus 46 terminating at a connection 50. By applying a potential between the terminals 48 and 50 a deflection field may be produced between each adjacent pair of the elements 40 and 42 so that a cathode-ray beam from the beam generating system 14, 16 and 18 (see Figure 1) normally directed toward a green stripe 34 may be deflected to impinge either a red stripe 32 or a blue stripe 36 depending on the relative polarities of the terminals 48 and 50.

In the arrangement shown, each wire element operated at one polarity is arranged between two wire elements operated at the opposite polarity so that the deflection field between consecutive pairs of electrodes is alternately reversed. This alternation of the deflection tield may be compensated by a corresponding alternation of the sequence of the phosphor stripes 32, 34 and 36 as shown in Figure 2. Since, in such a sequence of the phosphor stripes, there will be twice as many green stripes 34 as red stripes 32 or blue stripes 36, it is preferable to make the red and blue stripes twice as wide as the green stripes in order more readily to achieve color balance in the screen structure.

In addition to serving as the deflection electrodes of the color determining deflection system, the elements 40 and 42'may be made to serve further as. one component of an electron lens adapted to focus the electron beam as a tine spot at its point of impingement on the phosphor stripes. Such an electron lens may be formed by applying a suitable potential between the elements 40 and 42 in common and the aluminum coating 38, for example by means of a battery 52 having its positive pole con nected to the coating 38 through the terminal lead 39 and having its negative pole connected to the positive pole of source 24 and to the elements 40 and 42 as will later be described more fully.

In accordance with a feature ofthe invention, the color determining deflection system is energized by a selfgenerating independent signal source. The teun freef running oscillator, where used in this case, refers to the type of signal source here described, which operates independently of any external synchronizing signal. Such a signal source, shown. as54, may consist of a. feed-back oscillatoradapted to apply a sine wave deflection voltage between adjacent pairs of the elements 40 and 42. In a typical form the oscillator S4 may comprise a. discharge tube 56 having4 a cathode 58, a control grid 60 and an anode 62 interconnected in feed-back relationship by means of a Itapped inductance 64 forming the inductive branch of a lresonant circuit. In the arrangement shown, the capacitive branch of the resonant circuit is constituted by the capacitance of the elements 40 and 42. This capacitance has been shown in dotted-lines as capacitorV 66: shunting the coil 64.

Suitable operating potentials may be applied to the tube 56 in conventional manner. For example, the anode 62 may be supplied from a source of positive potential (not shown) through a choke coil 68, whereas the operating bias for the tube S6 may be established by means of a grid resistor 70. The elements 40 and 441 of the color determining deflection system may be connected to the battery 52 by a suitable lead interconnecting the negative pole of the battery and the tap of the inductor 64. Blocking capacitors 72, 74 and 76 may be provided to isolate the operating potentials of the tube from the operating potentials of tube 56.

The inductance of the coil 64 is chosen in wellknown manner relative to the value ofl capacitance 66.so that the source 54 oscillates at a frequency establishedby. the desired number of color changes to be elfected during each line scanning interval and by the desired color detail to be reproduced. For example, in the case of a system in which the cathode-ray tube has a horizontal scanning frequency equal to 15,750 c./s. in accordance with present d-ay standards for monochrome receivers and in which the screen structurel of the tube contains approximately 425l groups of phosphor stripes, the oscillator source54 may be made to operate at 7 mc./sec.

For producing a color. image on the faceplate-of the cathode-ray tube, there areV provided color signal input terminals 80, 82 and 84 which are supplied` fromy atelcvision receiver (notshown) with separate signals indica-V tive of the red, greenvand blue components of the televised scene, respectively. The system then operates to convert these three color signals into a wave havingthe color information arranged in time reference sequence so that the red information occurs when the deection voltage applied to the color determining deilection sys-Y tem has a sense and magnitude causing the cathode-ray beam to impinge the red stripes 32, thegreen information occurs when the deflection voltage has a sense and magr1itude causing the cathode-ray beam to impinge the`v green stripes 34, and the blue information occurs when the deflection voltage has a sense and magnitude causinglthe beam to impinge the blue stripes 36.

The conversion of the color signalsV into a wave having the color information arranged in a time reference sequence as determined by the color determining deflection system is achieved by means vof av modulation system, suitably energized by theY respective color signalsgiandby appropriately-phased modulating signals derived from'the deilection system. In the arrangement shown, the desired conversion is effected by modulators 86, 88 and 90 which may beY of conventional form and may each consist, for example, of' a dual grid thermionic tube, to one grid of which is. applied the color signal from one of terminals 80, 82 and 84, and to the other grid of which is applied an individual modulating signal which makes the modulator conductive only `during intervals when ther beam is made to impinge on the corresponding color stripe by the color determining delection system. More particularly, and for the image screen structure specifically shown in Figure 2, thered signal modulator 86 is made. conductive for an interval during which the potential of element 40 is morepositive than that of element 42 by an amount equal to one-half of the peak amplitude of the deflection voltage applied to the deflection elements, the blue signal modulator is made, conductive for an interval during which the potential of element 40 is more negative than that of the element 42 by an amount equal to one half of the peak amplitude of the deflection voltage applied to the deflection elements, and the green signal modulator 88 is made conductive during the intervening intervals. Under these conditions each of the modulators S6 and 90 is made conductive for a 120 interval during each cycle of the deflection voltage applied to the deflection elements 40 and 42, and the modulator 88 is made conductive for two 60 intervals during each cycle of the deflection voltage; the 60 conduction intervals of modulator 88y occurring between the 120 conduction intervals of the modulators 86 and 90.

The waveformsgof the modulating signals applied tothe modulatorsV 86, 88 andv 90 and their relationships to theV waveform of: the deection voltage appliedv to the deflection elements .40. and 42 have been shown in Figure 3. wherein the curve A represents the sine wave signal produced bythe oscillator 54 and applied to the deection elements 40y and 42, the curve B represents the waveform of the modulating signal applied to modulator 86, the curve C represents the waveform of the signal applied to modulator 88, and the curve D represents the waveform of the signal applied to modulator 90.

As will be noted from Figure 3 the modulating signal Br assumes a positive value bringing about conduction through modulator 86, for a interval initiated at the 30 phase positionof the sine Wave A. The signal C attainsv a positive valueproducing conduction through modulator-88y fortwo 60 intervals, one of the intervals being initiated at the phase position of the sine wave A and-the other of the intervals being initiated at the 33.0 phase position of the sine wave A. Thel signal D assumes a positivevalue producing conduction through modulator. 90 for a 120 interval initiated, at the 210 phase position of the sine wave A.

The resultant wave derived from the modulators; is applied as a control potential to the controly electrode 16 of the tube 10, whereby the intensity of the beam is varied in time sequence in an order and for durations as determined by the modulating signals applied to the modulators .andQby amounts proportional to the. amplitudes of the input signals at terminals 80, 82 and 84.

The modulating signals for actuating they modulators in the above noted synchronous relationship may be derived from the source 54 by means of a wave forming system 92 coupled to the source 54 through a bmer 94 and a phaser 96. Inone form, ythe system 92 may comprise a pentode tube 100 which, by means of a suitable bias voltage applied to the rst grid thereof, is operated under cutoff conditions for al1 values of the input signal thereof less than one-half of the peak value thereof.V By an appropriate adjustment of the potentials applied to the screen grid and anode, the tube may be made to exhibit a signal limiting action. Under these conditions an output signalof the `form shown at B in Figure 3, is. produced by the tube 100 when a sinusoidal voltage,

such as shown at A, is applied to the input of the tube from the phaser 96. By means of a similarly operated pentode tube 102 having its input supplied from the phaser 96 through a phase inverter 104, the modulating signal D may be produced. The system 92 further com prises two triode tubes 106 and 108 having their input circuits individually connected to the output circuits of the tubes 100 and 102 respectively. By connecting the output circuits of the tubes 106 and 108 in common as shown, the signal C may be derived from the signals B and D.

The buffer 94 may consist of an amplier of conventional form and may serve merely as an isolation stage, whereas the phaser 96, which may consist of a variable resistance-capacitance network of known form, may serve to adjust the phase of the signal applied to the system 92 and thereby adjust the absolute phase position of the modulating signals B, C and yD relative to the phase of the deflection voltage applied to the color determining deec tion system by the source 54.

While I have described my invention by means of specific examples and in a specilic embodiment, I do not wish to be limited thereto for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

What I claim is:

l. A cathode-ray tube system for reproducing the intelligence represented by a signal supplied thereto, said system comprising a cathode-ray tube having a source of a beam of charged particles, means to vary the intensity of said beam and a beam intercepting member, said beam intercepting member comprising a plurality of' groups of elemental areas having different response characteristics upon impingement by said charged particles, said groups of elemental areas recurring at a given periodicity, means for scanning said beam across said intercepting member, auxiliary deliecting means adapted to impinge said beam on said elemental areas selectively as said beam scans said intercepting member and comprising a plurality of groups of deliecting elements recurring at said given periodicity, means for applying to said auxiliary deflection means a periodic deflection signal recurrent at a rate which is determined independently of said supplied intelligence signal, means for applying said supplied intelligence signal to said beam intensity varying means, means for deriving a control signal from said means for applying said dellection signal, and means responsive to said derived signal for controlling the relative time phase position of said intelligence signal.

2. A cathode-ray tube system as claimed in claim 1 wherein the said elemental areas of each of said groups are arranged on the surface of said screen structure, and wherein the said auxiliary deflecting means comprises a plurality of electrode elements arranged in interleaved pairs and disposed between said screen structure and said beam source.

3. A cathode-ray tube system as claimed in claim 2 wherein the said elemental a-reas are in the form of stripes arranged in substantially parallel relationship and wherein said electrode elements are arranged substantially parallel to said stripes.

4. A cathode-ray tube system as claimed in claim l wherein said deection signal means comprises an oscillatory system embodying said auxiliary deflection means as a component thereof.

5. A cathode-ray tube system as claimed in claim 1 wherein said beam intercepting structure further comprises an electrically conducting stratum, wherein said auxiliary deecting system comprises spaced interleaved electrodes arranged in pairs substantially parallel to said stratum, and further comprising means to apply a potential between the said interleaved electrodes in common and the said conducting stratum.

6. A cathode-ray tube system as claimed in claim 1 wherein said intelligence signal comprises a plurality of 8 component portions arranged in consecutive order and said means responsive to said deflection signal comprises means to control the relative time phase positions of said component portions.

7. A cathoderay tube system for producing a color television image in response to a color television signal supplied thereto, said system comprising a cathode-ray tube having a source of a beam of charged particles, means to vary the intensity of said beam and a beam intercepting member, said beam intercepting member comprising a plurality of groups of stripes of fluorescent material, the stripes of each of said groups being adapted to pro duce light of diiferent colors upon impingement by said beam, said groups of phosphor stripes recurring at a given periodicity, means for scanning said beamV across said beam intercepting member, auxiliary deflecting means arranged in cooperative relationship to said beam intercepting member and adapted selectively to impinge said beam on said phosphor stripes as said beam scans said intercepting member, said auxiliary deecting means comprising a plurality of groups of deecting elements recurring at said given periodicity, means for applying to said auxiliary deflection means a periodic deection signal recurrent at a rate which is determined independently of said supplied color television signal, means for applying to said intensity control means an intelligence signal derived from said supplied color television signal and representative at consecutive time intervals of desired excitation of the consecutively scanned phosphor stripes of said groups, means for deriving a control signal from said deflection signal, and means responsive to said derived signal for controlling the relative time phase position of said intelligence signal.

8. A cathode-ray tub system as claimed in claim 7 wherein said deflection signal means comprises an oscillatory system embodying said auxiliary deecting means as a component thereof.

9. A cathode-ray tube system as claimed in yclaim 8 wherein said deliection signal means comprises a feedback oscillator system comprising an inductance, and wherein said deecting elements exhibit a capacitative impedance and are coupled to said inductance to form a circuit resonant at the frequency of said deliection signal.

10. A cathoderay tube system as claimed in claim 7 wherein said beam intercepting structure further comprises an electrically conducting coating on said phosphor stripes, wherein said auxiliary deflecting system comprises spaced interleaved electrodes arranged in pairs substantially parallel to said phosphor stripes and to said electrically conducting coating, and further comprising means to apply a potential between said interleaved electrodes in common and said conductive coating.

11. A cathode-ray tube system for producing a color television image, comprising a cathode-ray tube having a source of a beam of charged particles, means to vary the intensity of said beam and a beam intercepting member, said beam intercepting member comprising a plurality of groups of stripes of fluorescent material, the stripes of each of said groups producing light of three different primary colors upon impingement by said beam, said groups of stripes recurring at a given periodicity, means for scanning said beam across said beam intercepting member, auxiliary deliecting means comprising a plurality of groups of deecting elements recurring at said given periodicity, said deecting means being arranged in cooperative relationship to said beam intercepting member and being adapted selectively to impinge said beam on said phosphor stripes as said beam scans said intercepting member, means comprising a resonant circuit adapted to generate a sinusoidal signal, said auxiliary deliecting means constituting a component of said resonant circuit, sources of three signal waves each representative of a diiferent primary color component of the image to be reproduced, and means to supply said signal waves selectively to said beam intensity varying means in synchronism with the selective impingement of said beam on said phosphor stripes by said auxiliary deflection means, said latter means comprising modulating elements coupling said signals to said beam intensity varying means, means to derive from said sinusoidal signal three modulating signals phase displaced relative to each other, and means to apply said modulating signals to said modulating elements to thereby render said modulating elements consecutively conductive in synchronism with the auxiliary deection of said beam on said phosphorstripes under the inuence of said sinusoidal signal.

12. A cathode-ray tube system as claimed in claim 1l wherein said auxiliary detlecting system comprises a plurality of interleaved pairs of wire elements, and wherein said first of said modulating signals is in the form of a rectangular wave having a duration for an interval of approximately 120 of the period of the said sinusoidal signal, wherein the second of said modulating signals is in the form of a rectangular wave having a duration approximating an interval of 120 of the period of said sinusoidal signal and is phase displaced from said rst Wave by approximately 180, and wherein the third of said modulating signals comprises `a rectangular wave having two duration intervals each approximately 60 of the period of the said sinusoidal signal, the said duration intervals of the third modulation signal occurring during the periods between the duration intervals of said first and second modulating signals.

13. A cathode-ray tube system for producing a color television image, comprising a cathode-ray tube having a source of a beam of charged particles, means to vary the intensity of said beam and a beam intercepting member, said beam intercepting member comprising a plurality of groups of stripes of fluorescent material, the stripes of each of said groups producing light of three different primary colors upon impingement by said beam, said groups of stripes recurring at a given periodicity, means for scanning said beam across said beam intercepting member, auxiliary deflecting means arranged in cooperative relationship to said beam intercepting member and adapted selectively to impinge said beam on said phosphor stripes as said beam scans said intercepting member, said deecting means comprising a plurality of interleaved wire elements arranged in pairs recurring at said given periodicity and positioned substantially parallel to said phosphor stripes, an oscillator source of a sinusoidal signal, said source comprising an electron discharge tube having input and output electrodes, an inductance element interconnecting said input and output electrodes in feedback relationship and a capacitative element coupled to said inductive element and forming a resonant circuit therewith, said capacitative element being constituted by said interleaved wire elements, three modulating elements, means to apply to each of said modulating elements one of three video` signals each representative of a different primary color component of the image to be reproduced, a modulating signal generator intercoupling said sinusoidal signal source and said modulating elements, said generator comprising a first electron discharge tube having an input circuit coupled to said oscillator source and an output circuit coupled to a first one of said modulator elements and being adapted to produce a rectangular wave having a duration approximating an interval of 120 of the period of said sinusoidal signal, a second electron discharge tube having an input circuit coupled to said oscillator source and an output circuit coupled to a second one of said modulators and being adapted to produce a rectangular wave having a duration approximating an interval of 120 of said sinusoidal signal, said second rectangular wave being phase displaced from said first rectangular wave, and third and fourth electron discharge tube systems having individual input systems and having output systems connected in common to the third of said modulating elements, said third tube system having the input thereof coupled to the output of said rst tube system and said fourth tube system having the input thereof coupled to the output of said second tube system.

14. In combination with a cathode-ray tube for displaying television images in color which includes an electron gun having electrodes controlling the intensity of an electron beam produced thereby, a color-control grid comprising two mutually insulated interleaved sets of elongated linear conductors and a display screen adjacent to said grid and having deposited thereon strips of phosphors emissive on electron impact of light of three different component colors -additively producing White, a strip of one of said phosphors being electro-optically centered behind each electrode of one of said sets as viewed from said gun, a strip of another of said phosphors being so centered behind each of the electrodes of the other of said sets, and a strip of the third of said phosphors being disposed between each pair of strips of the other two phosphors, an inductor connected between said two sets of electrodes to form a resonant circuit, means including said resonant circuit for producing electrical oscillations of substantially the frequency to which said inductor and the interelectrode capacity of said sets of electrodes are resonant, Ia group of three gating circuits each including terminals for two input circuits and one output circuit. connections from all of said output circuit terminals to 4the beam-controlling lelectrodes of said electron gun,

connections for applying said oscillations to said resonant circuit, connections for applying said oscillations as gating signals in opposite phases to the terminals for one input circuit of each of two of said gating circuits, frequencydoubler means connected for excitation by said oscillations, and connections for applying the signals from said frequency-doubling means as gating signals to the terminals for one input circuit of the third gating circuit.

15. In combination: a color picture tube having a focusing and switching grille; and a free-running oscillator circuit for supplying a color switching signal to said grille, said oscillator having frequency determining elements which comprise a resonant circuit including the distributed capacitance of said grille.

16.v In combination: a color picture tube having a focusing and switching grille, a free-running oscillator circuit -for supplying a color switching signal to said grille, said oscillator having frequency determining elements which comprise a resonant circuit including the distributed capacitance of said grille; means for receiving color picture signals representing the different colors reproduced by said picture tube in response to said switching signal; and means responsive to said color switching signal to apply said color picture signals to said color picture tube in synchronism with the reproduction of said different colors by said tube. Y

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